I am having trouble at picking the right solar panel and accumulator for my Arduino based project which is a weather station.
More about the project - I am using Arduino Mega which draws maximum of 143mA (average is ~139mA). What I want to achieve is a stand-alone weather station powered from accumulator which would be charged obviously from solar panel. Here, I am having trouble in picking the right parts. So far I have been thinking about 6V/7Ah gel accumulator and a single 10W/12V solar panel. Is this the way to go? If not, what should I go for?
So far the battery has lasted over a month with 3 rainy/dark days in a row.
A have another Jeenode inside my house connected to an LCD to see the data.
Thank you very much for your reply Pauly.
About Jeenode, I can not use it as I am forced down to Bluetooth and I have to stick to it no matter what.
I bought this solar charger some time ago. I am aware of it but I am not sure what should I place on both sides of it
About the battery and solar panel. Those will not do for me obviously. That is why I asked if my solution - 12V/5W panel and 6V/7Ah - would work in my case or maybe it is even too much.
Well, if you have the same solar charger I do be aware of the warnings.
NOTE: This product is only designed for use with solar panels sold at the Adafruit store. We cannot guarantee this will work with solar panels purchased elsewhere. Please purchase this kit and panels from Adafruit to ensure optimized functionality!
For use with Adafruit Lipoly/LiIon batteries only! Other batteries may have different voltage, chemistry, polarity or pinout.
The only other advice I have is get your power consumption as low as you can.
See Nick's Power tutorial.
There's no way to know which would be the "right" panel and battery without knowing where you are. The "right" panel/battery if you're in San Diego probably won't be "right" if you're in Iqaluit. There's also the question of how much of an unobstructed view of the sky the panel will have during the day and what orientation you're going to use.
I agree with Pauly that you need to investigate low power sleep modes.
I am wondering why you are using a Mega. How many inputs do you really need for a weather station? Why can't you use a Nano, for example?
6v is actually very inconvenient. It is too low for the normal Arduino input through the barrel jack and it is too high for direct connection to the 5v pin.
As @whoru has said 3.7v can work - I presume he is using an Arduino that can run at 3.7v, or perhaps he is using a breadboarded Atmega 328.
If you want to use a regular Arduino then a 12v system would probably be simplest using a 12v lead-acid battery and a suitable solar panel.
You need to choose a solar panel that is big enough to provide an average (averaged over a winter month) output that comfortably exceeds the demands of your Arduino and the inefficiency of the battery system.
Your battery must have ample capacity to keep the system working over a succession of days with poor sunshine. How long that is will depend on where you live.
Keep in mind that the actual capacity of most batteries is about 50% of what it says on the label.
el_supremo:
I agree with Pauly that you need to investigate low power sleep modes.
I am wondering why you are using a Mega. How many inputs do you really need for a weather station? Why can't you use a Nano, for example?
Pete
Yea I guess I have to reevaluate my project...
The reason behind using Mega is the size of the project. I am measuring temperature (DHT22), pressure (BMP180), humidity (DHT22), wind speed, rain intensity. For DHT22 and BMP180 I need separate libraries. Also, I implemented SD Card to track weather (around 500 bytes library), Bluetooth module (another library), LCD 2x16 (another library) and RTC (library here once again). I had to use so many libraries that even tho I optimized my code as much as I could basing on this: Optimizing SRAM | Memories of an Arduino | Adafruit Learning System I could not fit my sketch into even Uno.
I am not using many outputs. I could even use Nano if it had memory as big as Mega.
Robin2:
6v is actually very inconvenient. It is too low for the normal Arduino input through the barrel jack and it is too high for direct connection to the 5v pin.
6V would be driven directly to Mega to power it up - Input Voltage (recommended) 7-12V. My Mega is currently running on 4 AAA batteries (4 x 1.5) so no problem in using 6V accumulator.
Well, so far my conclusion is to reevaluate my whole project when it comes to current draw - 140mA is way too much...
A 12volt solar panel and a 12volt/7Ah lead/acid battery seems a good choice.
If you combine that with e.g. a Pololu 5volt/500mA!! buck converter, and connect that directly to the 5volt line, the 150mA draw from the Arduino is then lowered to about 75mA from the battery.
That will give you a no-sun run time of a few days.
Still good to look at other less power-hungry solutions.
The size of the panel might be directly related to that.
Leo..
